Film-Tech Forum ARCHIVE: Projecting the Color Black

This is topic Projecting the Color Black in forum Ground Level at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=5;t=003193

Posted by Paul Finn (Member # 10726) on 06-12-2019, 07:42 AM:

Projecting black from a film frame creates an absence-of-light area in the projected image for the desired black area in the picture. Is an absence-of-light area also created from the projector in a digital picture for black scenes? Or, do DMDs or other imagers create black in a digital picture by another method (than absence-of-light) that is projected as part of the color/light picture parts?

Thanks,Paul Finn

Posted by Carsten Kurz (Member # 5396) on 06-12-2019, 07:50 AM:

Essentially, it is the same, however, most digital projectors do not manage to create the same amount of 'absence of light'. A black frame in film is usually not perfectly black as well - it has a limited maximum density, and the frame may show some minor scratches, holes, etc. as well. However, in general, film black is blacker than digital projector black.

In reality, it is a bit more complex. Modern digital projectors may cheat using variable irises, light source dimming, a dowser, whatever. However, most of that is not available in real DCI compliant digital cinema projectors.

- Carsten

Posted by Marcel Birgelen (Member # 6801) on 06-12-2019, 08:43 AM:

The very definition of black is the absence of light. A perfect black surface is a surface that reflects no (visible) light at all. Such a surface is currently only hypothetical, although we're able to make material that can come close nowadays.

DLP projectors essentially dump all unused light into a heat-sink and LCoS based projectors try to block all the unused light right at the imager itself. Those processes aren't perfect and some light eventually leaks out of the light engine, into the lens and onto the screen. That's why in current standard DCI, black is more like a constant, deep grey.

Like Carsten already mentioned, none of the current DCI compliant machines use tricks like irises or dynamic light sources, which can help to increase on/off contrast in certain scenes, but come with other problems. It's because of those problems, it's currently not certified to be used for DCI.

There is one noticeable exception here and that's the Dolby Vision setup (used almost exclusively in Dolby Cinema), which most likely uses something like a segmented integrator rod construction, where each segment can be individually dimmed. This trick is comparable to what can be achieved with local dimming, used by many modern LCD/TFT based screens, where the backlight consists not only out of a single light source, but many smaller light-zones which can be individually controlled.

Posted by Bobby Henderson (Member # 840) on 06-12-2019, 10:09 AM:

Laser projection works better at creating a deep black than traditional Xenon-based DLP digital projection. One of the Dolby Cinema trailers has a kind of funny tag line at the end, written in small type over a black screen, "the projector is still on."

LED jumbotron displays can easily create a true black since it's only a matter of turning off specific LEDs in the display. OLED TV sets at home work the same way, each pixel is specifically illuminated. Due to high cost and other technical challenges I think it's going to take at least another decade of development before we see LED screens going into commercial theaters on any sort of widespread basis.

Posted by William Kucharski (Member # 7246) on 06-24-2019, 02:50 AM:

quote: Bobby Henderson
Dolby Cinema trailers has a kind of funny tag line at the end, written in small type over a black screen, "the projector is still on."

Which always makes me a bit sad, as obviously it's intended to be white letters on a pure black screen, but instead it's always a pure black screen with lit corners from the floor exit lighting plus often lit top corners from other low-level lighting around the theater. [Frown]

Posted by Marcel Birgelen (Member # 6801) on 06-24-2019, 05:29 AM:

Try to see it in a country where AMC doesn't have exclusivity of the Dolby Cinema concept. [Wink]

If it is done properly, it is pretty stunning, compared to what we've become used to be "black" in DCI nowadays.

Posted by Justin Hamaker (Member # 2165) on 06-24-2019, 04:30 PM:

I understand that black is actually just the absence of light. But this means the areas of the screen which are black are actually white (or silver). When do we perceive them as black? Is it because of the proximity to other areas where are lit up?

Posted by Sean McKinnon (Member # 612) on 06-24-2019, 04:40 PM:

The projection screen appears white because it is reflecting light back at a minimum of a 1:1 ratio (unless its a high contrast or grey screen which will reflect light back at less than 1:1 and is often referred to as a "grey" screen) so when the room is dark and there is no light being reflected back to you the screen appears to be black.

Posted by Jim Cassedy (Member # 4115) on 06-24-2019, 06:30 PM:

quote: Bobby Henderson
One of the Dolby Cinema trailers has a kind of funny tag line at the
end, written in small type over a black screen, "the projector is still on."

When working at Dolby's screening room in San Francisco, they usually had
me run a short Dolby Vision™ intro/demo 'sizzle reel' before whatever else
they were screening. At the end it fades to black. (and I mean BLACK !! )

But if whatever clip that followed it was not in D-Vision, the jump in black
level as it switched from D-V™ BLACK to plain old DCP black was quite jarring.
Almost like night & day, no pun intended!

The effect even more pronounced due to the fact that their auditorium is almost
totally dark, and great care has been taken to keep whatever safety lighting was
necessary off the screen.

Since it's a manually run booth, with a fairly large viewing port, it's necessary to
work almost totally in the dark, the only illumination coming from the monitor
screens & Crestron system control panels. - - but the image quality is AMAZING.

Posted by Bobby Henderson (Member # 840) on 06-24-2019, 10:01 PM:

I wish some theater chains, beside only AMC, would (or could) install Dolby Cinema systems. I don't know what kind of deal Dolby has in place with AMC, but I think it sucks for AMC to be the only outlet for Dolby Cinema in the United States. I think it's possible for other theater chains to do a better job with the concept.

Compounding the problem further, it looks like AMC has pumped the brakes on any new Dolby Cinema @ AMC installations. Perhaps that has something to do with the debt level of AMC and its Chinese parent company, Wanda. AMC used to have a list of Dolby Cinema screens on its web site, along with a "coming soon" list of upcoming new screen installations. That page is gone. Dolby no longer has the interactive map showing theater locations with Dolby Atmos or Dolby Cinema. They do have a text-based listing of Dolby Cinema locations.

Posted by Mark J. Marshall (Member # 1409) on 06-25-2019, 11:22 AM:

For what it's worth, whenever we projected a film on Kodak's Vision Premier stock, it looked like the projector shut off when it went from our Feature Presentation snipe to the feature itself.

Some IB prints of cartoons I projected that had black on the picture (Lucy's hair in Charlie Brown for example) often looked like there were giant holes in the screen.

There's black and then there's blacker-than-black.